Van Eck Phreaking

Van Eck phreaking, also known as Van Eck radiation, is a form of eavesdropping in which special equipment is used to pick up side-band electromagnetic emissions from electronic devices that correlate to hidden signals or data to recreate these signals or data to spy on the electronic device. Side-band electromagnetic radiation emissions are present in (and with the proper equipment, can be captured from) keyboards, computer displays, printers, and other electronic devices.

In 1985, Wim van Eck published the first unclassified technical analysis of the security risks of emanations from computer monitors. This paper caused some consternation in the security community, which had previously believed that such monitoring was a highly sophisticated attack available only to governments; van Eck successfully eavesdropped on a real system, at a range of hundreds of metres, using just $15 worth of equipment plus a television set.

As a consequence of this research, such emanations are sometimes called "van Eck radiation", and the eavesdropping technique van Eck phreaking. Government researchers were already aware of the danger, as Bell Labs had noted this vulnerability to secure teleprinter communications during World War II and was able to produce 75% of the plaintext being processed in a secure facility from a distance of 80 feet (24 metres). Additionally, the NSA published ''Tempest Fundamentals, NSA-82-89, NACSIM 5000, National Security Agency'' (Classified) on February 1, 1982. Also, the van Eck technique was successfully demonstrated to non-TEMPEST personnel in Korea during the Korean War in the 1950s.

While phreaking is the process of exploiting telephone networks, it is used here because of its connection to eavesdropping. Van Eck phreaking of CRT displays is the process of eavesdropping on the contents of a CRT by detecting its electromagnetic emissions.

Basic principle

Information that drives the video display takes the form of high-frequency electrical signals. These oscillating electric currents create electromagnetic radiation in the RF range. These radio emissions are correlated to the video image being displayed, so, in theory, they can be used to recover the displayed image.

CRTs

In a CRT the image is generated by an electron beam that sweeps back and forth across the screen. The electron beam excites the phosphor coating on the glass and causes it to glow. The strength of the beam determines the brightness of individual pixels (see CRT for a detailed description). The electric signal which drives the electron beam is amplified to up to around one hundred volts from TTL circuitry. This high frequency, high voltage signal creates electromagnetic radiation that has, according to Van Eck, "a remarkable resemblance to a broadcast TV signal". The signal leaks out from displays and may be captured by an antenna, and once synchronization pulses are recreated and mixed in, an ordinary analog television receiver can display the result. The synchronization pulses can be recreated either through manual adjustment or by processing the signals emitted by electromagnetic coils as they deflect the CRT's electron beam back and forth.

In the paper, Van Eck reports that in February 1985 a successful test of this concept was carried out with the cooperation of the BBC
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